The present invention is related to optical networks, and more specifically, to the economic calculation of bit error rates (BER) for the transport frames of the emerging OTN (Optical Transport Network).
OTN (Optical Transport Network), the standards of which are defined by the ITU (International Telecommunications Union), represents an updating of the SONET/SDH networks with the WDM (Wavelength Division Multiplexing). Where SONET/SDH networks dealt with a single channel of optical signals over an optical fiber, OTN deals with the multiplicity of optical channels provided by the wavelength channels of WDM. OTN defines an optical transport hierarchy with enhanced operations, administration, maintenance, and provisioning (OAM&P) functions. Among the requirements is FEC (Forward Error Correction), by which data is encoded and decoded using a Reed-Solomon coding algorithm. FEC identifies errors in the optical signals transmitted through the network and corrects some of these errors.
Optical networks in general have back-up protection communications channels to provide alternative paths for the optical signals in case there is some fault in the working communications channel. A fault impedes the communications channel signals in some manner, e.g., the optical fiber carrying the operation communications channel might be cut or an element in the path of the communications channel might be experiencing difficulty. The optical signals are then switched from the original working channel to the protection channel. The switch might include a switch from one optical fiber to another.
To determine the amount of impediment on a communications channel, the bit error rate (BER) of the channel is used. The channel with the higher BER has the greater amount of impediment. In many networks the BERs of the working and protection channels are used to determine which channel is used as the working channel (and which is used as the protection channel).
In an OTN the data signals in a channel are protected by FEC which by its nature provides the BER of the network signals carried by the channel. The BERs of the communications channels can be used to select the working and protection channels. However, the FEC algorithm is complex and requires dedicated integrated circuits for optimum implementation and these integrated circuits are expensive. The costs for the FEC function alone may become quite high when the number of optical channels and fibers in an OTN is considered.
Thus the application of FEC should be considered judiciously and the present invention provides for a less expensive alternative to determine the BER of OTN signals.